Rheostat



(No Model.)

H. W. LEONARD.

RHEOSTAT.

No. 603,063A Patented Apr. 26, 1898.

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UNITED STATES PATENT EETCE.

HARRY VARD LEONARD, OF EAST ORANGE, NE\V JERSEY.

RH EO STAT.

SPECIFICATION forming part 0f Letters Patent N 0. 603,063, dated. April 26, 1898.

Application filed J'nly 28, 1896. Serial No. 600,748. (No model.)

To all whom it may concern.:

Be it known that I, HARRY WARD LEONARD, a citizen of the United States, residing at East Orange, in the county of Essex and State of New Jersey, have invented a certain new and useful Improvement in Rheostats, Electric Heaters, and Similar Apparatus, of which the following is a specification.

My invention relates to rheostats, heaters, and similar electrical apparatus in which electrical energy is intentionally converted into heat, and has especial reference to apparatus in which the support for the electrical conductor is an iron plate, from which the conductor is separated by a thin layer of insulating material.

One wellknown form of apparatus of this description is the so-called enamel rheostat, in which the conductor is adhesively attached to the iron plate by means of a vitreous material, so that the conductor is firmly held in close proximity to the plate and insulated therefrom by a continuous layer of insulating` material. In such enamel apparatus I have found that if a cast-iron plate be employed for the support the insulating-layer should not be very glassy, for the reason that such a coating directly upon cast-iron will result in the formation of pin-holes, blisters, the., in the coating. On the other hand, by the admixture of inert powderedmaterial-such as powdered silica, clay, magnesia, &c.-a solid layer is obtained which is hard, adhesive, and free from pin-holes, blisters, dac.; but such a coating will not resist high electromotive-force strains tending to pierce the insulation between the conductor and the plate as effectively as a more glassy layer would. Furthermore, if the material be quite vitreous and a sudden large current be sent through the conductor while the apparatus is cold the expansion of the conductor frequently ruptures the layer of vitreous material.

It will be understood that in apparatus where the supporting-plates are not of castiron the insulating-coating may consist of a layer of vitreous material, since detrimental chemical action and the formation of pinholes, blisters, (be. are not so troublesome as with cast-iron. It will also be understood that in apparatus intended for handling low electromotive forces, whether the supportingplate be of cast-iron or other material, the insulating-coating may consist only of the nonvitreous or partially-vitrilied layer, because with comparatively low electromotive forces the tendency to pierce the insulating-coating is very slight. As a general rule, however, l prefer to employ the two coatings and the cast-iron supporting-plates, because cast-iron is the cheapest material, readily formed into the desired shape, and having the required properties.

In another form of apparatus of the general type described the conductor is separated from the iron plate by a layer of material, such as Portland cement, which is dried and sometimes baked at a moderate heat, but not enough to melt it. The insulating qualities of the Portland cement are not nearly so good as the vitreous material of the enamel, and to secure proper insulation a thickness frequently of one-fourth inch of Portland cement becomes necessary. This thick wall of insulating material seriously interferes with the flux of heat from the conductor to the plate and theinsulation is more aifected by hygrometric conditions than the vitreous insulation of the enamel.

My invention overcomes these difficulties; and it consists in the preferred form in providing a castiron supporting-plate covered on one side with a layer of non-vitreous or partially-vitrified material, which is made ad* herent thereto by heat, and this layer is covered with a layer of vitreous material, which renders the combined insulating-coating nonabsorbent of moisture and of high insulating quality. Upon the vitreous surface when cold I place the conductor; but the conductor is not adhesively attached thereto, as has been heretofore customary. In order to hold the conductor in position in close proximity to the vitreous surface, I sometimes embed the conductor wholly or partially in a material, such as Portland cement, which becomes hard without having to be exposed to a temperature sufficient to fuse the vitreous material. Sometimes l use two plates with the vitreous surfaces toward each other and the conductor held between them in contact therewith, and in such case it is only necessary to ill up the spaces between the adjacent sections of the conductor with a suitable insu- IOO lating material to prevent contact between the adjacent sections. For such a material I may use materials which are practically inert at the working` temperature-such as clay, plaster-of-paris, cement, hef-or I may use spun glass, asbestos, mica, or other similar materials which may not be in powdered form.

One marked advantage of my invention is that in placing the conductor in position relative to the vitreous coating the conductor is not subjected to the detrimental heat of the muftle-furnace, as in the case with the enameled goods made by the present processes.

Another advantage is the comparative cheapness in making repairs, for if the conductor burns out the plate with its vitreous insulation is still as perfect as at first, and only the wire and the holding material need be renewed,which is a cheap operation as coinpared with any of the methods at present in use.

It will be apparent that in apparatus constructed in accordance with my invention the expansion of the heating-conductor does not injure or impair the insulation, because the conductor is not firmly held in the layer of insulation which separates it from the metal support and which is fused upon the surface of the metal support, and because my mode of attaching the conductor permits a slight but sufficient movement of the conductor d ue to any cause without affecting the efficiency of the apparatus.

The preferred form of my invention is illustrated in the accompanying` drawings. In Figure l the metal support A,such as castiron, has applied to it a ground coat B, which is preferably a partially-vitrilied material, preferably applied in the form of a powder, either dry or mixed with a fluid, so as to be paste-like or cement-like, or suspended in a liquid, so as to be paint-like, and which afterward, bythe application of heat or otherwise, becomes a coherent layer of solid material. The ground coat B is made impervious to moisture by a thin vitritied coating C, such as glass, applied in powdered form and made into a solid adhesive layer by heat, or it may be applied in any other form. The conductor D is placed upon the glass coat and is held in position by a non-vitrilied layer E, which may be Portland cement, clay, asbestos, spun glass, mica, or anj1 powdered infusible insulating material.

In Fig. 2 two metal plates are shown, but having similar layers of insulating material. The conductor is shown in contact with the two glass coats C, and the spaces between the conductor are closed by afilling E, which serves to prevent contact between adjacent sections of the conductor.

In Fig. 3 I have shown the conductor as wound upon a base F, which may be a slab of slate or other equivalent insulating material. The slab with the conductor is placed between two metal plates, coated as in Fig.

2, and the spaces between the conductor are closed, as in that Iigure, by a filling E.

In using the words vitreous7 or vitrified I mean a material which when subjected to the heat of manufacture becomes a solid coherent mass, impervious to moisture, like glass, porcelain, rbc., and by the words partially vitriiied I mean a material which is composed partially of glass or glass-forming materials and which, when subjected to a degree of heat sufficient to fuse the glass or glass-forming materials, will become a coherent mass, due to the glass or glass-forming materials acting as a binder, but without producing a glassy surface, and which material is more or less moisture-absorbent, like pottery, brick, (he. By non-vitreous or non-vitried I mean a material which is not subjected to heat sufficient to fuse any of the particles.

lVhile in the drawings I have shown a round conductor, it will be evident that any other form of conductor may be employed without departing from the spirit of my invention, and I therefore wish it to be understood that I do not limit myself to the shape or to any particular arrangement of the conductor upon the support.

l. The combination of a support covered by a layer of partially-vitriiied insulating material, a layer of vitreous insulating material on said layer, and a conductor held to the insulated side of the support by a layer of non-vitrified insulating material.

2. The combination of a cast-iron support covered by a layer of partially-vitriiied insulating material, a layer of vitreous insulating material on said layer, and a conductor held to the insulated side of the support by a layer of non-vitritied insulating material.

8. The combination with two plates or supports having a layer of part-ially-vitrified insulating material, and a covering-layer of vitreous insulating material, of a conductor held between said insulated plates.

et. The combination with two plates orsupports having a layer of partially-vitrified insulating material, and a covering-layer of vitreous insulating material, of a conductor held between said insulated plates, and a filling of non-vitrilied material between the adjacent sections of the conductor.

5. The combination with two east iron plates or supports having a layer of partiallyvitriiied insulating material, and a coveringlayer of vitreous insulating material, of a conductorheld between said insulated plates.

G. The combination of a metalsupport, covered by a layer of insulating material, applied as a powder and made by heat into a coherent mass adhesive to the support, a glazing of vitreous material on said layer, and a conductor held to the support by a layer of nonvitried insulating material.

'7. The combination of a cast-iron support,

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covered by two layers of insulating material, the rst layer being applied as a powder and made by heat into a coherent mass adhesive to the support, the second layer being applied in the form of powdered glass which by heat is caused to fuse and produce a glaze on the first layer, and a conductor held to the support by a layer of non-vitriiied insulating material.

8. The combination of a metal support covered by a layer of vitreous insulating material, and a conductor held to the support by a layer of non-vitriiied insulating material.

9. The combination of a metal support, covered by a layer of vitreous insulating material, and a conductor held to the support by a layer of cement.

10. The combination of a cast-iron support, covered by a layer of partially-vitriiied insulating material, a layer of vitreous material on the first layer, and a conductor held to the support by a layer of cement.

11. The combination of a conductor carried by a support of insulating material and a metal plate placed in close proximity thereto, said plate being insulated from said conductor by a layer of vitreous material.

12. The combination of a conductor carried by a support of insulating material and a metal plate placed in close proximity thereto, said plate being insulated from said conductor by a layer of vitreous material, and a llin g of non-vitreous material between ad jacent sections of the conductor.

13. The combination of a conductor carried by a support of insulating material, and a cast-iron plate placed in close proximity thereto, said plate being insulated from said conductor by a layer of partially-vitrifled material covered by a second layer of vitreous material, and a filling of non-vitreous material between the adjacent sections of the conductor.

14. The combination of a conductor carried by a support of insulating material, and two metal plates between which said support with the conductors is placed,`the inner surfaces of said plates being insulated from said conductor by a layer of vitreous material.

15. The combination of a conductor carried by a support of insulating material, and two metal plates between which said support with the conductor is placed, the inner surfaces of said plates being insulated from said conductor by a layer of vitreous material, and a lling of non-vitreous material between the adjacent sections of the conductor.

16. The combination of a conductor carried by a support of insulating material, and two cast-iron plates between which said support with the conductor is placed, the inner surfaces of said plates being insulated from said conductor by a layer of partially-vitriiied material covered by a second layer of vitreous material, and a filling of non-vitreous material between the adjacent sections of the conductor.

17. The combination of a metal support having upon its surface two layers of adherent insulating material, each separately applied as a powder and made adherent by heat, and a heating-conductor insulated from the metal support by said insulating-layers but free to expand without affecting the said insulating-layers.

18. The combination of a metal support, a ground coat applied as a powder and made adherent by heat, a glaze upon said ground coat and a conductor in contact with said glazed surface but free to expand without affecting the said glazed surface.

19. A conductor held in position by a thin layer of insulating material between two metal surfaces, each of the two surfaces being coated by an adherent layer of insulating niaterial applied as a powder and made adherent to the surfaces by heat.

20. The combination of a box-like support coated on the inside with a layer of insulating material, a conductor arranged on said layer of insulating material,and a plate placed over said support and whose inner side is covered by a layer of insulating material.

21. The combination of a cast-iron box-like support coated on the inner side by a layer of partially-vitriiied material, a coating of vitreous insulating material on said first layer, a conductor arranged on said vitreous layer, and a plate placed over said box-like support and coated on its inner side with a layer of insulating material.

This specification signed and witnessed this 25th day of July, 1896.

HARRY VARD LEONARD.

Witnesses:

W. PELzER, EUGENE CoNRAN.

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